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Add some simplifications for demanded bits, this allows instcombine to turn:

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define i64 @test(i64 %A, i32 %B) {
        %tmp12 = zext i32 %B to i64             ; <i64> [#uses=1]
        %tmp3 = shl i64 %tmp12, 32              ; <i64> [#uses=1]
        %tmp5 = add i64 %tmp3, %A               ; <i64> [#uses=1]
        %tmp6 = and i64 %tmp5, 123              ; <i64> [#uses=1]
        ret i64 %tmp6
}

into:

define i64 @test(i64 %A, i32 %B) {
        %tmp6 = and i64 %A, 123         ; <i64> [#uses=1]
        ret i64 %tmp6
}

This implements Transforms/InstCombine/add2.ll:test1


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34919 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-03-05 00:02:29 +00:00
parent bc62f24a8c
commit 783ccdb5c4
1 changed files with 31 additions and 0 deletions
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31
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -1186,6 +1186,37 @@ bool InstCombiner::SimplifyDemandedBits(Value *V, uint64_t DemandedMask,
// Bits are known zero if they are known zero in both operands and there
// is no input carry.
KnownZero = KnownZero2 & ~RHSVal & ~CarryBits;
} else {
// If the high-bits of this ADD are not demanded, then it does not demand
// the high bits of its LHS or RHS.
if ((DemandedMask & VTy->getSignBit()) == 0) {
// Right fill the mask of bits for this ADD to demand the most
// significant bit and all those below it.
unsigned NLZ = CountLeadingZeros_64(DemandedMask);
uint64_t DemandedFromOps = ~0ULL >> NLZ;
if (SimplifyDemandedBits(I->getOperand(0), DemandedFromOps,
KnownZero2, KnownOne2, Depth+1))
return true;
if (SimplifyDemandedBits(I->getOperand(1), DemandedFromOps,
KnownZero2, KnownOne2, Depth+1))
return true;
}
}
break;
case Instruction::Sub:
// If the high-bits of this SUB are not demanded, then it does not demand
// the high bits of its LHS or RHS.
if ((DemandedMask & VTy->getSignBit()) == 0) {
// Right fill the mask of bits for this SUB to demand the most
// significant bit and all those below it.
unsigned NLZ = CountLeadingZeros_64(DemandedMask);
uint64_t DemandedFromOps = ~0ULL >> NLZ;
if (SimplifyDemandedBits(I->getOperand(0), DemandedFromOps,
KnownZero2, KnownOne2, Depth+1))
return true;
if (SimplifyDemandedBits(I->getOperand(1), DemandedFromOps,
KnownZero2, KnownOne2, Depth+1))
return true;
}
break;
case Instruction::Shl: